Examples of well-known, conventional, and highly metal-chelating resins include "Duolite ES466" (product name of an ion-exchange resin available from Rohm & Haas Co.) and "Diaion CR11" (product name of an ion-exchange resin available from Mitsubishi Chemical Corp.). These resins contain an iminodiacetic acid group, and further contain a carboxylic group and an highly electron-donative nitrogen atom in a principal chain of a functional group.
However, those conventional resins undergo proton exchanges under low pH and therefore decline in metal-chelating ability. In addition, the amount of metal ions scavenged (chelated) by the resins of a unitary weight is not satisfactory. Hence there is a large demand for a resin with a superior metal-ion-scavenging ability (chelating ability).